Add collection types for IR children

src/Microsoft.AspNetCore.Mvc.Razor.Extensions/InjectDirectiveIRNode.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Language.CodeGeneration;
 using Microsoft.AspNetCore.Razor.Language.Intermediate;
@@ -15,7 +14,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Extensions
 
         public string MemberName { get; set; }
 
-        public override IList<RazorIRNode> Children { get; } = new RazorIRNode[0];
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Extensions/TemplateIRNode.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Language.CodeGeneration;
 using Microsoft.AspNetCore.Razor.Language.Intermediate;
 
@@ -10,7 +9,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
 {
     public sealed class TemplateIRNode : ExtensionIRNode
     {
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/AddPreallocatedTagHelperHtmlAttributeIRNode.cs

@@ -2,14 +2,13 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Language.CodeGeneration;
 
 namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     internal sealed class AddPreallocatedTagHelperHtmlAttributeIRNode : ExtensionIRNode
     {
-        public override IList<RazorIRNode> Children { get; } = EmptyArray;
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/AddTagHelperHtmlAttributeIRNode.cs

@@ -11,7 +11,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/CSharpCodeAttributeValueIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/CSharpCodeIRNode.cs

@@ -23,7 +23,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/CSharpExpressionAttributeValueIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/CSharpExpressionIRNode.cs

@@ -23,7 +23,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/ChecksumIRNode.cs

@@ -1,8 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using System.Collections.Generic;
-using System.Security.Cryptography;
 using System.Text;
 
 namespace Microsoft.AspNetCore.Razor.Language.Intermediate
@@ -11,7 +9,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children => EmptyArray;
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/ClassDeclarationIRNode.cs

@@ -23,7 +23,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/CreateTagHelperIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children { get; } = EmptyArray;
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DeclarePreallocatedTagHelperAttributeIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     internal sealed class DeclarePreallocatedTagHelperAttributeIRNode : ExtensionIRNode
     {
-        public override IList<RazorIRNode> Children { get; } = EmptyArray;
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DeclarePreallocatedTagHelperHtmlAttributeIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     internal sealed class DeclarePreallocatedTagHelperHtmlAttributeIRNode : ExtensionIRNode
     {
-        public override IList<RazorIRNode> Children { get; } = EmptyArray;
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DeclareTagHelperFieldsIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children { get; } = EmptyArray;
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DefaultIRNodeCollection.cs

@@ -0,0 +1,128 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+
+namespace Microsoft.AspNetCore.Razor.Language.Intermediate
+{
+    public sealed class DefaultIRNodeCollection : RazorIRNodeCollection
+    {
+        private readonly List<RazorIRNode> _inner = new List<RazorIRNode>();
+
+        public override RazorIRNode this[int index]
+        {
+            get
+            {
+                if (index < 0 || index >= Count)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(index));
+                }
+
+                return _inner[index];
+            }
+            set
+            {
+                if (index < 0 || index >= Count)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(index));
+                }
+
+                _inner[index] = value;
+            }
+        }
+
+        public override int Count => _inner.Count;
+
+        public override bool IsReadOnly => false;
+
+        public override void Add(RazorIRNode item)
+        {
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            _inner.Add(item);
+        }
+
+        public override void Clear()
+        {
+            _inner.Clear();
+        }
+
+        public override bool Contains(RazorIRNode item)
+        {
+            return _inner.Contains(item);
+        }
+
+        public override void CopyTo(RazorIRNode[] array, int arrayIndex)
+        {
+            if (array == null)
+            {
+                throw new ArgumentNullException(nameof(array));
+            }
+
+            if (arrayIndex < 0 || arrayIndex > array.Length)
+            {
+                throw new ArgumentOutOfRangeException(nameof(arrayIndex));
+            }
+            else if (array.Length - arrayIndex < Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(arrayIndex));
+            }
+
+            _inner.CopyTo(array, arrayIndex);
+        }
+
+        public override IEnumerator<RazorIRNode> GetEnumerator()
+        {
+            return _inner.GetEnumerator();
+        }
+
+        public override int IndexOf(RazorIRNode item)
+        {
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            return _inner.IndexOf(item);
+        }
+
+        public override void Insert(int index, RazorIRNode item)
+        {
+            if (index < 0 || index > Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(index));
+            }
+
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            _inner.Insert(index, item);
+        }
+
+        public override bool Remove(RazorIRNode item)
+        {
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            return _inner.Remove(item);
+        }
+
+        public override void RemoveAt(int index)
+        {
+            if (index < 0 || index >= Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(index));
+            }
+
+            _inner.RemoveAt(index);
+        }
+    }
+}

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DesignTimeDirectiveIRNode.cs

@@ -9,7 +9,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     internal sealed class DesignTimeDirectiveIRNode : ExtensionIRNode
     {
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DirectiveIRNode.cs

@@ -24,7 +24,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DirectiveTokenIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children { get; } = EmptyArray;
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DocumentIRNode.cs

@@ -24,7 +24,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public string DocumentKind { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/FieldDeclarationIRNode.cs

@@ -23,7 +23,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
-        public override IList<RazorIRNode> Children { get; } = EmptyArray;
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public IList<string> Modifiers { get; set; } = new List<string>();
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/HtmlAttributeIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/HtmlAttributeValueIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/HtmlContentIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/MethodDeclarationIRNode.cs

@@ -23,7 +23,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/NamespaceDeclarationIRNode.cs

@@ -23,7 +23,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/PropertyDeclarationIRNode.cs

@@ -23,7 +23,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
-        public override IList<RazorIRNode> Children { get; } = EmptyArray;
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public IList<string> Modifiers { get; set; } = new List<string>();
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/RazorIRNode.cs

@@ -11,7 +11,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 
         public abstract ItemCollection Annotations { get; }
 
-        public abstract IList<RazorIRNode> Children { get; }
+        public abstract RazorIRNodeCollection Children { get; }
 
         public abstract RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/RazorIRNodeCollection.cs

@@ -0,0 +1,40 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections;
+using System.Collections.Generic;
+
+namespace Microsoft.AspNetCore.Razor.Language.Intermediate
+{
+    public abstract class RazorIRNodeCollection : IList<RazorIRNode>
+    {
+        public abstract RazorIRNode this[int index] { get; set; }
+
+        public abstract int Count { get; }
+
+        public abstract bool IsReadOnly { get; }
+
+        public abstract void Add(RazorIRNode item);
+
+        public abstract void Clear();
+
+        public abstract bool Contains(RazorIRNode item);
+
+        public abstract void CopyTo(RazorIRNode[] array, int arrayIndex);
+
+        public abstract IEnumerator<RazorIRNode> GetEnumerator();
+
+        public abstract int IndexOf(RazorIRNode item);
+
+        public abstract void Insert(int index, RazorIRNode item);
+
+        public abstract bool Remove(RazorIRNode item);
+
+        public abstract void RemoveAt(int index);
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return GetEnumerator();
+        }
+    }
+}

src/Microsoft.AspNetCore.Razor.Language/Intermediate/RazorIRToken.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 
 namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
@@ -10,7 +9,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children => RazorIRNode.EmptyArray;
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public string Content { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/ReadOnlyIRNodeCollection.cs

@@ -0,0 +1,133 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Microsoft.AspNetCore.Razor.Language.Intermediate
+{
+    public sealed class ReadOnlyIRNodeCollection : RazorIRNodeCollection
+    {
+        public static readonly ReadOnlyIRNodeCollection Instance = new ReadOnlyIRNodeCollection();
+
+        private ReadOnlyIRNodeCollection()
+        {
+        }
+
+        public override RazorIRNode this[int index]
+        {
+            get
+            {
+                if (index < 0 || index >= Count)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(index));
+                }
+
+                throw null; // Unreachable
+            }
+            set
+            {
+                if (index < 0 || index >= Count)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(index));
+                }
+
+                throw null; // Unreachable
+            }
+        }
+
+        public override int Count => 0;
+
+        public override bool IsReadOnly => true;
+
+        public override void Add(RazorIRNode item)
+        {
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            throw new NotSupportedException();
+        }
+
+        public override void Clear()
+        {
+            throw new NotSupportedException();
+        }
+
+        public override bool Contains(RazorIRNode item)
+        {
+            return false;
+        }
+
+        public override void CopyTo(RazorIRNode[] array, int arrayIndex)
+        {
+            if (array == null)
+            {
+                throw new ArgumentNullException(nameof(array));
+            }
+
+            if (arrayIndex < 0 || arrayIndex > array.Length)
+            {
+                throw new ArgumentOutOfRangeException(nameof(arrayIndex));
+            }
+            else if (array.Length - arrayIndex < Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(arrayIndex));
+            }
+
+            throw new NotSupportedException();
+        }
+
+        public override IEnumerator<RazorIRNode> GetEnumerator()
+        {
+            return Enumerable.Empty<RazorIRNode>().GetEnumerator();
+        }
+
+        public override int IndexOf(RazorIRNode item)
+        {
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            return -1;
+        }
+
+        public override void Insert(int index, RazorIRNode item)
+        {
+            if (index < 0 || index > Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(index));
+            }
+
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            throw new NotSupportedException();
+        }
+
+        public override bool Remove(RazorIRNode item)
+        {
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            return false;
+        }
+
+        public override void RemoveAt(int index)
+        {
+            if (index < 0 || index >= Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(index));
+            }
+
+            throw new NotSupportedException();
+        }
+    }
+}

src/Microsoft.AspNetCore.Razor.Language/Intermediate/SetPreallocatedTagHelperPropertyIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     internal sealed class SetPreallocatedTagHelperPropertyIRNode : ExtensionIRNode
     {
-        public override IList<RazorIRNode> Children { get; } = EmptyArray;
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/SetTagHelperPropertyIRNode.cs

@@ -11,7 +11,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/TagHelperBodyIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/TagHelperIRNode.cs

@@ -23,7 +23,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/UsingStatementIRNode.cs

@@ -10,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
-        public override IList<RazorIRNode> Children { get; } = EmptyArray;
+        public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override RazorIRNode Parent { get; set; }
 

test/Microsoft.AspNetCore.Razor.Language.Test/CodeGeneration/DesignTimeBasicWriterTest.cs

@@ -549,9 +549,10 @@ Render Node - CSharpExpressionIRNode
 
         private class MyExtensionIRNode : ExtensionIRNode
         {
-            public override IList<RazorIRNode> Children => throw new NotImplementedException();
+            public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
             public override RazorIRNode Parent { get; set; }
+
             public override SourceSpan? Source { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
 
             public override void Accept(RazorIRNodeVisitor visitor)

test/Microsoft.AspNetCore.Razor.Language.Test/CodeGeneration/RuntimeBasicWriterTest.cs

@@ -650,7 +650,7 @@ WriteAttributeValue("" "", 27, false, 28, 6, false);
 
         private class MyExtensionIRNode : ExtensionIRNode
         {
-            public override IList<RazorIRNode> Children => throw new NotImplementedException();
+            public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
             public override RazorIRNode Parent { get; set; }
             public override SourceSpan? Source { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }

test/Microsoft.AspNetCore.Razor.Language.Test/Intermediate/DefaultRazorIRBuilderTest.cs

@@ -216,7 +216,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
         {
             public override ItemCollection Annotations { get; } = new DefaultItemCollection();
 
-            public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+            public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
             public override RazorIRNode Parent { get; set; }
 

test/Microsoft.AspNetCore.Razor.Language.Test/Intermediate/ExtensionIRNodeTest.cs

@@ -44,7 +44,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 
         private class TestExtensionIRNode : ExtensionIRNode
         {
-            public override IList<RazorIRNode> Children => throw new NotImplementedException();
+            public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
             public override RazorIRNode Parent { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
             public override SourceSpan? Source { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }

test/Microsoft.AspNetCore.Razor.Language.Test/Intermediate/RazorIRNodeWalkerTest.cs

@@ -72,7 +72,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 
             public override ItemCollection Annotations { get; } = new DefaultItemCollection();
 
-            public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+            public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
             public override RazorIRNode Parent { get; set; }